The present invention relates to a process for removing impurities from a fluid stream, in particular, the present invention is directed to removing suspended solids from a waste water stream exiting a wet rendering plant, a centrifugal rendering plant, a hide brine curing system, or the like.
A common by-product of essentially every rendering or hide curing type process is a water stream containing substantial quantities of fat or oil, protein material, and solids. A number of processes have been developed for recovering fat from such water streams and for removing solids which are easily settled out of such streams. Examples of such processes are included in the patents of Lee R. Lyon, PROCESS FOR OBTAINING OIL FROM ANIMAL HIDES U.S. Pat. Ser. No. 3,338,931, PROCESS FOR SEPARATING AND RECOVERING FATS AND SOLIDS, U.S. Pat. Ser. No. 3,352,841, and PROCESSING OF OFFAL OR THE LIKE FOR OBTAINING SEPARATED FAT AND PROTEIN MATERIAL THEREFROM, U.S. Pat. Ser. No. 3,352,842. While conventional processes have proved satisfactory in the past for removing certain contaminents or impurities in a water stream sent to the sewer or the like, stricter environmental regulations and a typically increased cost of despositing suspended solids into a sewer system, have demonstrated a need to remove additional suspended solids from waste water streams which have not been removed by previous conventional processes.
When utilized in rendering plants, the process according to the present invention typically is directed to treating waste water with substantial portions of fat, protein, and easily settled solids previously removed therefrom. Such waste water resulting from rendering processes is commonly referred to as "stick-water." The process is also directed to treating waste brine effluent streams from the brine curing of hides and the offending impurities within the waste water typically include fat, protein, suspended dirt and manure solids removed from such hides during the curing process.
Conventional wet rendering and centrifugal rendering plant waste water treatment processes typically tend to fail to remove the suspended solids and such solids often by-pass the conventional water treatment or cleaning processes within the plant. Therefore, the present process has been developed to remove such suspended solids. It should be noted that even where local laws and regulations allow inclusion of suspended solids and biological oxygen demanding substances (BOD) within a waste water stream, that there is often an additional sewage charge based upon the amount of suspended solids and BOD within such flow streams. Further, most local laws and regulations prohibit the discharge of any fats and oils or the like in excess of a relatively very small percentage of the liquid effluent and, because of this, the typical rendering plant effluent is often in violation of such local laws.
Therefore, it is advantageous to remove as high a percentage as possible of such suspended solids. It is also noted that the suspended solids in the waste water stream have typically not lent themselves to filtration processes, basically because a large portion of the suspended solids is composed of particles typically too small to filtrate and/or the volume of particles to be removed makes fine filtration impracticle, even after removal of agglomerated particles by other methods. Thus, such filters tend to be clogged or plugged, and even flocculated solids tend to pass or squeeze through filter media, when effluent is passed through the filter in large quantities, such that the filter media must be relatively porous.